The present invention is a process for the production of organosilanes from the high-boiling residue resulting from the reaction of organohalides with silicon metalloid in a process typically referred to as the "direct process." The present process comprises forming a mixture comprising an organotrihalosilane and the high-boiling residue in the presence of hydrogen gas, a hydrogenolysis catalyst, and a redistribution catalyst. The organotrihalosilane and high-boiling residue are converted into commercially useful organosilanes, particularly di- and triorganohalosilanes and organohydrosilanes. The present process results in consumption of the organotrihalosilane rather than a net increase which typically occurs upon hydrogenolysis of the residue in the absence of the redistribution catalyst.
In the preparation of organohalosilanes, various polysilane products are formed during the reaction and remain in the residue after the separation of the monosilanes. For example, in the commercial method known as the "direct process," in addition to the monosilanes, which in the case of the chloromonosilanes include dimethyldichlorosilane, methyltrichlorosilane, and trimethylchlorosilane there is always obtained a variety of compounds which boil above the monosilanes, that is above about 70.degree. C., which is hereafter referred to as "high-boiling residue." The "direct process" is well described in the patent literature, for example, in Rochow, U.S. Pat. No. 2,380,995, issued Aug. 7, 1945, and Barry et al., U.S. Pat. No. 2,488,487, issued Nov. 15, 1949. The residue after removing the monosilanes is a complex mixture of compounds that include SiSi, SiOSi, and SiCSi linkages in the molecules. Typical residues are described in Mohler et al., U.S. Pat. No. 2.598.435. issued May 27, 1952. and Barry et al., U.S. Pat. No. 2,681,355. issued Jun. 15, 1954.
In current commercial operations for performing the direct process, the high-boiling residue can constitute as much as five percent of the resultant product. Therefore, it is desirable to convert the high-boiling residue into commercially desirable products to both reduce waste disposal and to improve raw material utilization.
Wagner, U.S. Pat. No. 2.606,811, issued Aug. 12, 1952, teaches a hydrogenolysis process where a compound containing a halogen and the Si--Si bond is heated to a temperature of at least about 300.degree. C. in the presence of hydrogen. The resultant products are monosilanes.
Atwell et al., U.S. Pat. No. 3 639.105, issued Feb. 1, 1972, describes a process where hydrosilanes are produced by contacting a disilane with hydrogen gas under pressure and heating the mixture in the presence of a transition metal catalyst such as palladium on charcoal. When the disilane was a methylchlorodisilane, the resulting product contained about four to 28 weight percent of methytrichlorosilane. Generally, organotrihalosilanes such as methytrichlorosilane have limited commercial usefulness and for this reason limit the usefulness of the process described by Atwell et al.
Neale, U.S. Pat. No. 4,079,071, issued Mar. 14, 1978, describes a process for preparing high yields of hydrosilanes by reacting methylchloropolysilanes with hydrogen gas under pressure at a temperature of from about 25.degree. C. to about 350.degree. C. in the presence of a copper catalyst. Useful copper catalysts described by Neale include copper metal, copper salts, and complexes of copper salts with organic ligands. Neale reports an experiment in which the level of methyltrichlorosilane was elevated to about 12 weight percent of a disilane mixture. This mixture, containing the elevated level of methytrichlorosilane, was contacted with hydrogen gas and a Raney nickel catalyst for one hour at 350.degree. C. Neale concluded that no substantial change in product distribution occurred particularly in regard to the level of methyltrichlorosilane.
Therefore, in view of Neale and of Atwell et al., unexpectedly the inventors have discovered a process in which the addition of organotrihalosilane to the process results in a net consumption of the organotrihalosilane, as opposed to the production of organotrihalosilane as previously reported.
Ritzer et al.. U.S. Pat. No. 4.393 229, issued Jul. 12, 1983, describes a process for converting the alkyl-rich disilanes in the residue obtained from the manufacture of alkylhalosilanes to halogen-rich polysilanes with alkyltrihalosilanes. The process simultaneously converts the alkyltrihalosilanes to dialkyldihalosilanes by reacting the alkyl-rich polysilanes in the residue and the alkyltrihalosilanes at an elevated temperature in the presence of a suitable catalyst and a catalytic amount of a hydrosilane reaction promoter. Ritzer et al. reported a preferred embodiment to be treating the residue containing alkyl-rich disilanes with methyltrichlorosilane at a temperature of about 100.degree. C. to about 250.degree. C. in the presence of aluminum trichloride and a catalytic amount of methyldichlorosilane. Although Ritzer et al. report the use of the redistribution catalyst, aluminum chloride, to effect a redistribution between disilanes and an organotrihalosilane, they do not recognize that this reaction can be combined with a hydrogenolysis process to achieve the beneficial results described herein.
The object of the present invention is to provide a process where the high-boiling residue from a direct process for producing organosilanes can be converted into commercially useful organosilanes while resulting in a net consumption of organotrihalosilanes.